1. Field of the Invention
The present invention relates to a structure of an electronic apparatus provided with a metal core substrate mounting electronic parts thereon, and a manufacturing technique thereof.
It is necessary that the electronic apparatus provided with the electronic substrate is structured such as to generate no defect caused by a heat generation by the electronic parts. Accordingly, a heat cycle test is executed before shipping. In particular, in an electronic part for vehicle used such as an ECU or the like, it is affected by whether or not an LSI chip generates heat due to an engine on or off in addition to a temperature change within a vehicle body in accordance with a change of environment or the like, and it is necessary that the electronic part or the like stands against a thermal cycle (for example, −40 degrees to 120 degrees: environmental test general rule JAS0D001 of electronic device for motor vehicle) in a wide temperature range. In recent years, there is a tendency that the ECU is arranged close to the engine, that is, there is a tendency that an upper limit of the temperature range becomes higher. When being exposed to the thermal cycle mentioned above a performance of the electronic parts within the ECU becomes unstable, and a connection defect between the mounting substrate for the electronic parts and the electronic parts tends to be generated. That is, a high heat radiating performance is required in the electronic apparatus, and more particularly, a heat radiating performance which is more excellent than that of the general electronic part is required in the electronic part for vehicle use such as the ECU or the like.
A prior art relating to a structure of a general electronic apparatus taking into consideration heat generation of the electronic part mounted on the substrate includes JP-A-6-169189.
In this publication, there is described an electronic circuit board in which a pad for a heat radiating electrode connected to a ground via a through hole is formed on a printed circuit board having the ground in an inner layer, and the pad for the heat radiating electrode and the heat radiating electrode provided in a chip type heat generating part are mounted so as to align. The structure of the electronic circuit board secures a heat radiating performance of the printed circuit board by radiating a heat generated by the chip type heat generating part to the ground via the heat radiating electrode, the pad for the heat radiating electrode and the through hole.
Further, there is a metal core substrate as a substrate for general electronic parts, and there is JP-A-7-326690 as a prior art taking into consideration a heat radiating performance of the metal core substrate.
In this publication, there is described a matter that an internal wiring pattern is formed on the metal core substrate, an outer lead is connected to the internal wiring pattern, the internal wiring pattern is formed by processing a thin film, for example, etching a copper film or the like, and a portion on which a chip part of the metal core substrate on which the internal wiring pattern is formed is mounted is formed in a recess portion.
JP-A-6-169189 describes neither a heat radiating structure corresponding to a kind of a substrate nor a metal core substrate since a glass epoxy material is used as a core of the substrate. Further, since a ground terminal of a semiconductor part is also set to a fixed size in the same manner as the other signal terminals, it is not sufficient to secure a heat radiating performance.
Further, in JP-A-7-326690, since a metal core substrate is used, a heat diffusion efficiency of the substrate itself is improved, however, since an organic adhesive agent such as an epoxy resin or the like or an organic insulating layer such as a polyimide or the like is provided between the metal core substrate and the electronic part, a heat conductivity from the electronic part to the substrate is low. That is, it is not said that the heat conductivity from the electronic part to the mounting substrate is sufficiency considered.
Further, no consideration is given to a connection defect between a semiconductor part terminal and a wiring which is generated in the case of forming the wiring on the metal core substrate in accordance with the prior art and employing a flip chip type semiconductor part in the wired metal core substrate.
Further, no consideration is given to a heat radiating structure in the case of mounting an electronic substrate to the other substrate as an interposer or the case of a multi chip module (MCM) in which a plurality of chips are mounted.